The present invention relates to an apparatus for controlling periodic flashings of vehicle directional lamps and particularly to an improvement in the generation of pulses which control the periodic flashings of the directional lamps.
It is known well in the turn-direction indicating system of an automotive vehicle that a group of front, rear and side directional lamps are energized in response to periodic pulses to flash periodically upon requirement for the indication of vehicle turning direction. It is also known that the frequency of the periodic pulses is increased upon disconnection of the front or rear directional lamp to increase flashing frequency of the remaining directional lamps.
One of this system is disclosed in the prior art, U.S. Pat. No. 3,858,177 issued on Dec. 31, 1974, in which front and rear directional lamps are connected in parallel with each other and connected in series with a battery, a current detecting resistor, a relay and a turn-direction selecting switch and an electronic circuit including a flip-flop is provided to generate periodic pulses applied to the relay. The electronic circuit is connected to the turn-direction selecting switch so that, when the flip-flop is rendered operative in response to the closure of the selecting switch, the periodic pulses are generated.
According to this kind of electric connection between the electronic circuit and the turn-direction selecting switch, the electronic circuit is likely to generate the periodic pulses erroneously when the flip-flop is accidentally rendered operative or inoperative in response to electric noise signals which are induced on long electric wirings extending from the battery to the directional lamps. To obviate this erroneous operation, it is suggested to provide a capacitor at such a portion as the input side of the flip-flop (specification, column 9, lines 22-38). However, due to the difficulty in integrating the capacitor into an integrated semiconductor chip, the capacitor inevitably must be provided outside the semiconductor chip. This results in an increase in manufacturing cost.